1. Field of the Invention
The present invention relates to a bis-arylphenoxy catalyst system for producing ethylene homopolymers or ethylene copolymers with alpha-olefins, and more particularly to a group-IV transition metal catalyst shown in Formula 1, which comprises a cyclopentadiene derivative around a group-IV transition metal and two aryloxide ligands substituted with aryl derivatives at the ortho-positions, the ligands not being bridged to each other, as well as a catalyst system comprising said bis-arylaryloxy transition metal catalyst and an aluminoxane co-catalyst or a boron compound co-catalyst, and a method for producing ethylene homopolymers or ethylene copolymers with α-olefins using said catalyst:
wherein M is a group-IV transition metal in the periodic table; Cp is cyclopentadienyl or a derivative thereof, which can η5-bind to the metal center; R1, R2, R3, R4, R5, R6, R7, R8 and R9 on the arylphenoxide ligands are each independently a hydrogen atom, a halogen atom, a C1-C20 linear or nonlinear alkyl group optionally substituted with at least one halogen atoms, a silyl group containing a C1-C20 linear or nonlinear alkyl group optionally substituted with at least one halogen atoms, a C6-C30 aryl group optionally substituted with at least one halogen atom, an C7-C30 arylalkyl group optionally substituted with at least one halogen atom, an alkoxy group having a C1-C20 linear or nonlinear alkyl group optionally substituted with at least one halogen atoms, a siloxy group having C3-C20 alkyl or C6-C20 aryl, an amido or phosphido group having a C1-C20 hydrocarbon group, or a mercapto or nitro group having C1-C20 alkyl, and may also optionally bind to each other to form a ring; and X is selected from the group consisting of an halogen atom, a C1-C20 alkyl group other than a Cp derivative, a C7-C30 arylalkyl group, an alkoxy group having a C1-C20 alkyl group, a siloxy group having C3-C20 alkyl, and an amido group having a C1-C20 hydrocarbon group.
2. Description of the Prior Art
In the production of ethylene homopolymers or ethylene copolymers with α-olefins according to the prior art, a so-called Ziegler-Natta catalyst system consisting of a main catalyst component of a titanium or vanadium compound and a co-catalyst component of an alkyl aluminum compound has generally been used. The Ziegler-Natta catalyst system shows high activity for ethylene polymerization, but has problems in that, due to the heterogeneity of catalytic active sites, the molecular weight distribution of produced polymers is generally wide, and the composition distribution is not uniform, particularly in copolymers of ethylene with α-olefin.
Recently, a so-called metallocene catalyst system consisting of a metallocene compound of periodic table group-IV transition elements (e.g., titanium, zirconium, hafnium, etc.) and co-catalyst methylaluminoxane has been developed. Because the metallocene catalyst system is a homogeneous catalyst having a single species of catalytic active site, it has a characteristic in that it can produce polyethylene having a narrow molecular weight distribution and uniform composition distribution, compared to the existing Ziegler-Natta catalyst system. For example, European Patent Publication No. 320,762 or 277,004 and Japanese Patent Publication No. Sho 63-092621, Hei 02-84405 or Hei 03-2347 disclose a metallocene compound such as Cp2TiCl2, Cp2ZrCl2, Cp2ZrMeCl, Cp2ZrMe2 or ethylene (IndH4)2ZrCl2, activated with co-catalyst methylaluminoxane, that can polymerize ethylene at high activity to produce polyethylene having a molecular weight distribution (Mw/Mn) of 1.5-2.0. However, it is known that it is difficult for said catalyst system to obtain high-molecular-weight polymers, and said catalyst system is unsuitable for the production of high-molecular-weight polymers having a weight-average molecular weight (Mw) of more than 100,000, because, particularly when it is applied in solution polymerization conducted at a high temperature of more than 140° C., the polymerization activity thereof will be rapidly reduced and β-dehydrogenation reactions will predominate.
Meanwhile, as a catalyst capable of producing high-molecular-weight polymers at high catalytic activity in solution polymerization conditions for ethylene homopolymerization or ethylene copolymerization with α-olefins, a so-called “constrained geometry catalyst” (single active site catalyst) having a transition metal connected to a ring structure has been reported. European Patent Publication Nos. 0416815 and 0420436 disclose an example in which an amide group is connected to a cyclopentadienyl ligand in the form of a ring structure, and European Patent Publication No. 0842939 shows an example of a catalyst in which a phenol compound as an electron donor compound is connected with a cyclopentadiene ligand in the form of a ring structure. However, because the yield of ring formation reaction between the ligand and the transition metal compound in a step of synthesizing this constrained geometry catalyst is very low, it is very difficult to commercially use the constrained geometry catalyst.
On the other hand, an example of a catalyst, which is a non-metallocene catalyst, but not a constrained geometry catalyst, and, at the same time, can be used in high-temperature conditions, is disclosed in U.S. Pat. No. 6,329,478 and Korean Patent Publication No. 2001-0074722. In these patents, it can be seen that a single active site catalyst having a phosphinimine compound as a ligand shows high ethylene conversion in the copolymerization of ethylene with α-olefin in a high-temperature solution polymerization condition of more than 140 °C. However, for the synthesis of the phosphinimine ligand, a restrictive phosphine compound should be used, which is very difficult to use for general-purpose olefin polymers, because it is harmful to the human body and to the environment. U.S. Pat. No. 5,079,205 discloses an example of a catalyst having a bis-phenoxide ligand, and U.S. Pat. No. 5,043,408 discloses an example of a catalyst having a chelated bisphenoxide ligand, but these catalysts have too low activity, and thus are difficult to commercially use for the production of ethylene homopolymers or ethylene copolymers with α-olefins, which is conducted at high temperatures.
In addition to the above examples, an example relating to the synthesis of a phenolic ligand as a non-metallocene catalyst and the use thereof in polymerization was reported in the literature “Organometallics 1998, 17, 2152 (Nomura, et al.)”, but this example is limited to an isopropyl group, a simple alkyl substituent, and is thus different from an arylaryloxy catalyst according to the present invention with respect to structural and electronic properties. Also, there is no mention of polymerization reactivity at high temperature. On the other hand, the case of an arylphenoxy ligand is mentioned in the literature “J. Organomet. Chem. 1999, 591, 148 (Rothwell, P. et al.)”, but this literature did not recognize the effect of an aryl substituent at the ortho-position and does not show the concrete application of the ligand as a catalyst for polymerization.